The space age is barely two decades old, but the steps taken during that time have created unparallelled opportunities for the exploration and use of outer space. The space shuttle has been a step which has greatly facilitated this opportunity.
The space shuttle is a versatile vehicle having the essential characteristics of a spacecraft; yet is, in some respects, similar to an aircraft. The shuttle ascends into outer space with the assistance of rockets just as does the conventional spacecraft and descends from outer space, in a manner reminiscent of the landing of an aircraft, by gliding through the atmosphere and landing on a runway. The development of the shuttle is a significant achievement because it marks the advent of a rudimentary space transportation system. The system is expected to enable man and cargo to "shuttle" routinely to and from outer space, thereby making it possible to service, repair and resupply spacecraft, to build larger structures, such as industries, and eventually to construct settlements in outer space.
In a technical sense, the space shuttle is made up of an orbiter containing the shuttle main engines, an external tank containing the ascent propellant used by the orbiter's main engines, and two solid rocket boosters. The orbiter and the solid rocket boosters are reuseable, while the external tank is expendable on each launch. At launch, the two solid rockets and the orbiter's three liquid rocket engines ignite and burn simultaneously. The orbiter, with its crew and payload, remains in orbit to carry out a mission, normally for about seven days, but when required for as long as thirty days. When the mission is completed, the orbiter returns to Earth and lands like an airplane.
While the space shuttle marks a major step forward in the development of outer space, there are a number of problems which prevent the most effective, economical and efficient method of operating such a shuttle system. Heretofore, the prior art shows little effort to refine the space shuttle to provide greater flexibility.
One of the main problems with the space shuttle is that the orbiter, the spacecraft which looks like a Delta-winged airplane about the size of a DC-9 jetliner, must attach to an external tank and systems burden and also contain three liquid rocket engines and their associated systems. The fuel container, residual fuels at termination of the primary burn, and the rocket engines add a considerable amount of mass to the total going into or approaching orbit.
Furthermore, and even more importantly, the engines and the fuel arrangement minimize the amount of cargo space within the orbiter. This means that smaller and lighter payloads are required. Although the orbiter can deliver up to 25 tons of internal payload to orbit, the internal payload is only 1/7 of the total mass placed into orbit.
Another problem with the shuttle is the fact that the external tank for the three main engines is jettisoned in flight. Since the cost of each of these tanks is considerable, and the manufacturing capacity limited, it would appear to be desirable to avoid destruction of this tank on every flight of the space shuttle. Also, the effective use of the space shuttle orbiter is limited by the fact that it must carry this large tank almost into Earth Orbit with it.
Space shuttle orbiters contain both the payload bay and the main engines. Since they are both expensive and complex to build, there will normally be relatively few orbiters in operation at any one time. Transport to space is limited when orbiters are inoperative for maintenance or while they are in orbit. Thus, for example, orbiters cannot be used for long duration manned space missions without severely restricting launch capacity. They must be brought back to earth quickly to support launch operations. This constrains in-orbit research and could critically limit the delivery and assembly of space station or other major space projects.
These and other problems are currently being encountered by the space shuttle. In times when money was unlimited for the space program, it may have been unnecessary to exercise efficiency and economy with the projected operation of such a shuttle program. But today, in view of the limited budgets for space exploration, and the need for private enterprise space exploration, the efficiency and economy problems associated with space shuttle operation and further development are impossible to ignore.